1. Field of the Invention
The present invention relates to a gas generator composition used in a gas generator for generating a large volume of gas in relatively short period of time. A container may be attached, for example, to the steering wheel of an automobile in order to inflate an air bag.
2. Description of the Related Art
With the growing public demand for safer automobiles, air bags are more frequently found as a standard feature in new cars sold today. These gas inflated devices are well known as passive restraint systems used to reduce the injuries caused to automobile occupants in event of a car collision. Such air bags are commonly attached to the steering wheel or front dash panel in the car's passenger compartment. A main component of these air bag systems is the gas generator composition employed in order to inflate the air bag. Conventionally known gas generator compositions primarily contain sodium azide and various types of oxidizing agents, and are typically molded into pellets or rods. This generator composition is incorporated into a metallic case such as of stainless steel and aluminum, and when burned, generates nitrogen gas which inflates the air bag.
While the present composition is particularly suitable for inflating air bags in automobiles, it can also be utilized an application where a large amount of gas is required such as an inflatable raft. Such a composition can also be utilized for inflating an air bag employed in a passenger escape chute of an airplane.
To date, the preferred gas generator primarily contains sodium azide which produces clean nitrogen gas when burned. Unfortunately, sodium azide is itself highly toxic and readily hydrolysis to form hydrogen azide. Hydrogen azide is also highly toxic and explosive as well. In addition, sodium azide and hydrogen azide are likely to form volatile and explosive substances when brought in contact with acids or heavy metals.
Accordingly, in order to easily handle compositions containing azide compounds, special care must be taken during the production, storage and utilization of the compound. Moreover, the compositions essentially containing sodium azide produce, upon combustion, large amounts of corrosive residues such as sodium and sodium compounds. These compounds must be effectively treated and converted to noncorrosive compounds before they are discarded.
In order to solve these problems, efforts have been made to produce a gas generator composition containing no sodium azide. For example, Japanese Patent Publication No. 20919/1983 discloses a composition comprising the following three components: (1) an oxidizing agent, (2) a cellulose acetate and (3) a carbon-containing combustion controller. More specifically, the composition contains (1) 78 to 92% by weight of a chlorate or perchlorate of an alkali metal or alkaline earth metal as the oxidizing agent, (2) 7.9 to 17.2% by weight of a cellulose acetate and (3) 0.1 to 0.8% by weight of a carbon-containing combustion controller.
As a carbon-containing combustion controller, for example, acetylene black or graphite is used. This composition typically generates about 0.36 lit/g of a gas consisting primarily of water, carbon dioxide and oxygen, for example, under the normal conditions.
However, the composition described in the above patent publication has a very high combustion temperature. Accordingly, when the composition is used in a gas generator container the generated gas must be cooled to prevent the air bag from burning etc. Thus, a large amount of cooling agent must be provided in the gas generator container for the above compositions. This requirement effectively prevents manufacturers from being able to reduce the size of the conventional gas generator container.
Size and weight reduction for gas generator containers can generally be achieved in a more sophisticated manner by increasing the amount of gas to be generated per unit .weight of the composition. This reduces the amount of the gas generator composition necessary per gas generator container. However, such downsizing or weight reduction has not fully been achieved yet. Another disadvantage of previous gas generator compositions is that they produce harmful carbon monoxide.